It is a requirement that auto-injectors signal to the user when the injection is complete. Most have a visible indication, but sometimes the injection site is out of sight or would require some straining to see, for example in the buttocks or upper arm. It is therefore desirable to have an audible or tactile ‘injection complete’ signal. The term ‘injection complete’ is used to refer to a condition in which a satisfactory delivery of the drug has been achieved.